Gas Cluster Processing Device and Gas Cluster Processing Method

ABSTRACT

There is provided a gas cluster processing device for performing a predetermined process on a workpiece by irradiating the workpiece with a gas cluster, including: a processing container in which the workpiece is disposed; a gas supply part configured to supply a gas for generating the gas cluster; a flow rate controller configured to control a flow rate of the gas supplied from the gas supply part; a cluster nozzle configured to receive the gas for generating the gas cluster at a predetermined supply pressure, spray the gas into the processing container maintained in a vacuum state, and convert the gas into the gas cluster through an adiabatic expansion; and a pressure control part provided in a pipe between the flow rate controller and the cluster nozzle and including a back pressure controller configured to control a supply pressure of the gas for generating the gas cluster.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 U.S.C § 371 national stage filling ofInternational Application No. PCT/JP2018/004669, filed Feb. 9, 2018, theentire contents of which are incorporated by reference herein, whichclaims priority to Japanese Patent Application No. 2017-057086, filed onMar. 23, 2017, the entire contents of which are incorporated byreference herein.

TECHNICAL FIELD

The present disclosure relates to a gas cluster processing device and agas cluster processing method.

BACKGROUND

In the process of manufacturing a semiconductor device, particlesadhering to a substrate cause product defects. Thus, a cleaning processis performed to remove the particles adhering to the substrate. As atechnique for performing such a substrate cleaning process, a techniqueof irradiating the surface of the substrate with a gas cluster to removeparticles adhering to the surface of the substrate by virtue of thephysical action of the gas cluster has attracted attention.

As a technique for irradiating a substrate surface with a gas cluster,there is known a technique which includes spraying a cluster generationgas, such as CO₂, from a nozzle in a vacuum while keeping the gas at ahigh pressure, generating a gas cluster by adiabatic expansion, ionizingthe generated gas cluster in an ionization part, accelerating theionized gas cluster by an acceleration electrode, and irradiating thesubstrate with a gas cluster ion beam formed by the acceleration (see,for example, Patent Document 1).

Further, there is known a technique which includes spraying a pluralityof gases including a cluster generation gas such as CO₂ and anacceleration gas such as He from a nozzle in a vacuum and irradiating asubstrate with a neutral gas cluster generated by adiabatic expansion(see, for example, Patent Document 2).

The diameter of the gas cluster irradiated from the nozzle is determinedby a supply pressure of the gas. Thus, it is necessary to control thegas supply pressure. As disclosed in Patent Documents 1 and 2, the gassupply pressure has been mainly controlled based on the supply flow rateof the gas. That is to say, since the gas supply pressure and the gassupply flow rate are in a proportional relationship with each other, itis possible to control the gas supply pressure by controlling the gassupply flow rate. In addition, as disclosed in Patent Document 2, fineadjustment of the supply pressure is performed using a pressureadjustment valve.

PRIOR ART DOCUMENT Patent Documents

-   Patent Document 1: Japanese Laid-Open Patent Publication No.    2006-500741-   Patent Document 2: Japanese Laid-Open Patent Publication No.    2013-175681

The gas supply flow rate is controlled using a mass flow controller(which obtains a temperature change proportional to a mass flow rate ofa gas in an inner flow path, converts the temperature change into anelectric signal, and operates a flow rate control valve based on anelectric signal corresponding to an externally set flow rate to controlthe gas supply flow rate to the set flow rate). In the flow rate controlusing the mass flow controller, it takes a long period of time to reachthe set pressure. When it is attempted to shorten a period of time takento reach the set supply pressure by increasing the gas supply amount tobe more than a supply amount corresponding to the set supply pressure,the supply pressure overshoots with respect to a pressure set by thepressure adjustment valve, which degrades a pressure controllability. Inaddition, when such an overshoot occurs, a pressure at the downstreamside of the mass flow controller is increased so that a difference inpressure between front and back sides of the mass flow controller is notobtained. This makes it difficult to perform the control of the gassupply amount itself.

Therefore, the present disclosure provides a technique that is capableof reaching a gas supply pressure required for generating a gas clusterin a short period of time when irradiating a substrate with the gascluster to perform a process on the substrate, and controlling the gassupply pressure with enhanced controllability.

SUMMARY

According to a first aspect of the present disclosure, there is provideda gas cluster processing device for performing a predetermined processon a workpiece by irradiating the workpiece with a gas cluster,including: a processing container in which the workpiece is disposed; agas supply part configured to supply a gas for generating the gascluster; a flow rate controller configured to control a flow rate of thegas supplied from the gas supply part; a cluster nozzle configured toreceive the gas for generating the gas cluster at a predetermined supplypressure, spray the gas into the processing container maintained in avacuum state, and convert the gas into the gas cluster through anadiabatic expansion; and a pressure control part provided in a pipebetween the flow rate controller and the cluster nozzle and including aback pressure controller configured to control a supply pressure of thegas for generating the gas cluster.

The pressure control part includes a branch pipe branched from the pipe.The back pressure controller is provided in the branch pipe and isconfigured to exhaust the gas from the pipe therethrough. A primary-sidepressure of the back pressure controller is set to the predeterminedsupply pressure. It is possible to exhaust excess gas through the backpressure controller when the primary-side pressure reaches thepredetermined supply pressure.

The back pressure controller includes a first back pressure controllerand a second back pressure controller which are provided in the branchpipe in a serial manner. A high-precision back pressure controllerhaving a relatively narrow pressure difference range is used as thefirst back pressure controller. A primary-side pressure of the firstback pressure controller may be set to be a set value of the gas supplypressure. A back pressure controller having a pressure difference rangewider than the pressure difference range of the first back pressurecontroller is used as the second back pressure controller. Aprimary-side pressure of the second back pressure controller may be setto be lower than the set value of the gas supply pressure.

The gas cluster processing device may further include a controllerconfigured to control a set flow rate of the flow rate controller. Thecontroller controls the set flow rate of the flow rate controller to afirst flow rate exceeding a flow rate required for reaching thepredetermined supply pressure until the supply pressure of the gassupplied from the gas supply part reaches the predetermined supplypressure. The pressure control part may include a flowmeter configuredto measure a flow rate of a gas flowing through the back pressurecontroller. The controller may control, based on the measured valueobtained by the flowmeter, the set value of the flow rate controller toa second flow rate which is greater than a flow rate enough to maintainthe predetermined supply pressure and less than the first flow rate.

The gas supply part may be configured to separately supply at least twotypes of gases as the gas for generating the gas cluster. The flow ratecontroller may include at least two flow rate controllers providedrespectively to correspond to the at least two types of gases. The atleast two types of gases may be joined in the pipe at downstream sidesof the at least two flow rate controllers. The pressure control part maybe provided in a portion of the pipe in which the at least two types ofgases are joined.

The gas cluster processing device may further include a booster providedat an upstream side of a portion of the pipe in which the pressurecontrol part is provided, the booster being configured to increase apressure of the gas for generating the gas cluster. Further, thepressure control part may further include a bypass flow path provided tobypass the back pressure controller from the pipe, and anopening/closing valve configured to open/close the bypass flow path.After the gas cluster is processed, the opening/closing valve may beopened to exhaust the gas remaining in the cluster nozzle and the pipethrough the bypass flow path. The gas cluster processing device mayfurther include a temperature adjusting part provided at the downstreamside of the branch pipe in which the pressure control part is disposedand configured to adjust the temperature of the gas remaining in thecluster nozzle and existing at the upstream side of the cluster nozzle.The flow rate controller may be a mass flow controller.

The first flow rate may be controlled to fall within a range of 1.5times to 50 times the flow rate enough to maintain the predeterminedsupply pressure. The second flow rate may be controlled to fall within arange of 1.02 to 1.5 times the flow rate enough to maintain thepredetermined supply pressure.

According to a second aspect of the present disclosure, there isprovided a gas cluster processing method of performing a predeterminedprocess on a workpiece by supplying a gas for generating a gas clusterto a cluster nozzle through a pipe, spraying the gas from the clusternozzle into a processing container maintained in a vacuum state,converting the gas into the gas cluster by an adiabatic expansion, andirradiating the workpiece disposed inside the processing container withthe gas cluster. The method includes controlling a flow rate of the gasto a predetermined flow rate, discharging a portion of the gas from thepipe, and controlling a supply pressure in the pipe to a predeterminedsupply pressure.

In the second aspect, the supply pressure may be controlled using a backpressure controller. In this case, the back pressure controller isprovided in a branch pipe branched from the pipe such that the gasdischarged from the pipe flows into the back pressure controller throughthe branch pipe. A primary-side pressure of the back pressure controllermay be set to be the predetermined supply pressure. When theprimary-side pressure reaches the predetermined supply pressure, anexcess gas may be discharged through the back pressure controller.Further, the back pressure controller may include a first back pressurecontroller and a second back pressure controller which are provided inthe branch pipe in a serial manner. A high-precision back pressurecontroller having a narrow pressure difference range may be used as thefirst back pressure controller. The primary-side pressure of the firstback pressure controller may be set to be a set value of the gas supplypressure. A back pressure controller having a pressure difference rangewider than the pressure difference range of the first back pressurecontroller may be used as the second back pressure controller. Theprimary-side pressure of the second back pressure controller may be setto be lower than the set value of the gas supply pressure.

The gas cluster processing method may further include: controlling a setflow rate of the flow rate controller to a first flow rate required forreaching the predetermined supply pressure until the supply pressure ofthe gas reaches the predetermined supply pressure; measuring a flow rateof the gas discharged from the pipe and flowing through the backpressure controller; and controlling, based on the measured flow rate,the flow rate of the gas to a second flow rate greater than a flow rateenough to maintain the predetermined supply pressure and less than thefirst flow rate. In the case, the first flow rate may be controlled tofall within a range of 1.5 times to 50 times the flow rate enough tomaintain the predetermined supply pressure, and the second flow rate maybe controlled to fall within a range of 1.02 to 1.5 times the flow rateenough to maintain the predetermined supply pressure.

According to the present disclosure, the flow rate of the gas suppliedfrom the gas supply part is controlled by the flow rate controller. Thegas supply pressure for generating the gas cluster in the pipe betweenthe flow rate controller and a cluster nozzle is controlled by apressure control part having a back pressure controller. Thus, bycausing the gas for generating the gas cluster to flow at a large flowrate, it is possible to discharge excess gas when reaching apredetermined supply pressure, and it is possible to reach thepredetermined gas supply pressure in a short period of time. Inaddition, as described above, since the excess gas is discharged whenthe predetermined supply pressure is reached, no overshoot occurs at thegas supply pressure, and since the gas supply pressure is maintainedconstant during the cleaning process by the back pressure controller,the controllability of the gas supply pressure is satisfactory.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view illustrating a gas cluster processingdevice according to a first embodiment of the present disclosure.

FIG. 2 is a view representing the relationship between a gas supplypressure and a gas supply flow rate.

FIG. 3 is a view representing a time-dependent change in supply pressurein a conventional case in which a gas supply pressure is controlledusing a gas supply flow rate.

FIG. 4 is a view representing a time-dependent change in pressure when agas supply amount is increased to be more than a supply amountcorresponding to a set supply pressure in the conventional case in whichthe gas supply pressure is controlled by the gas supply flow rate.

FIG. 5 is a flow chart illustrating an example of a gas supply pressurecontrolling method of the present disclosure.

FIG. 6 is a cross-sectional view illustrating a gas cluster processingdevice according to a second embodiment of the present disclosure.

FIG. 7 is a cross-sectional view illustrating a gas cluster processingdevice according to a third embodiment of the present disclosure.

FIG. 8 is a cross-sectional view illustrating a gas cluster processingdevice according to a fourth embodiment of the present disclosure.

FIG. 9 is a cross-sectional view illustrating a gas cluster processingdevice according to a fifth embodiment of the present disclosure.

FIG. 10 is a cross-sectional view illustrating a gas cluster processingdevice according to a sixth embodiment of the present disclosure.

FIG. 11 is a cross-sectional view illustrating a conventional gascluster processing device.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure will be described indetail with reference to the accompanying drawings.

First Embodiment

First, a first embodiment will be described. FIG. 1 is a cross-sectionalview illustrating a gas cluster processing device according to a firstembodiment of the present disclosure.

A gas cluster processing device 100 of the present embodiment isprovided to perform a cleaning process on a surface of a workpiece byirradiating the surface of the workpiece with a gas cluster.

The gas cluster processing device 100 includes a processing container 1that defines a processing chamber for performing the cleaning process.In the vicinity of the bottom portion in the processing container 1, asubstrate stage 2 for placing a substrate S thereon is provided.

Examples of the substrate S may include various substrates such as asemiconductor wafer and a glass substrate for a flat panel display, andare not particularly limited.

In the upper portion of the processing container 1, a cluster nozzle 11for irradiating a gas cluster towards the substrate S is provided toface the substrate stage 2. The cluster nozzle 11 includes a main body11 a and a conical tip 11 b. An orifice having a diameter of, forexample, about 0.1 mm is provided between the main body 11 a and the tip11 b.

The substrate stage 2 is driven by a drive part 3. When the substratestage 2 is driven by the drive part 3, relative movement occurs betweenthe substrate S and the cluster nozzle 11. The drive part 3 isconfigured as an XY table including an X-axis rail 3 a and a Y-axis rail3 b. The cluster nozzle 11 may be driven in a state where the substratestage 2 is fixedly provided.

An exhaust port 4 is formed in the bottom portion of the processingcontainer 1. An exhaust pipe 5 is connected to the exhaust port 4. Avacuum pump 6 is provided in the exhaust pipe 5. The interior of theprocessing container 1 is evacuated by the vacuum pump 6. A degree ofvacuum at the time of the evacuation may be controlled by a pressurecontrol valve 7 provided in the exhaust pipe 5. A combination of theexhaust pipe 5, the vacuum pump 6, and the pressure control valve 7constitutes an exhaust mechanism 10. The interior of the processingcontainer 1 is maintained at a predetermined degree of vacuum of, forexample, 0.1 to 300 Pa, by the exhaust mechanism 10.

A loading/unloading port 8 through which the substrate S is loaded andunloaded is formed on the side surface of the processing container 1.The processing container 1 is connected to a vacuum transfer chamber(not illustrated) through the loading/unloading port 8. Theloading/unloading port 8 is opened/closed by a gate valve 9. Theloading/unloading of the substrate S with respect to the processingcontainer 1 is performed by a substrate transfer device (notillustrated) inside the vacuum transfer chamber.

The cluster nozzle 11 is connected to one end of a gas supply pipe 12which penetrates through a ceiling wall of the processing container 1 tosupply a cluster generation gas, which is a gas for generating a gascluster inside the cluster nozzle 11. The other end of the pipe 12 isconnected to a gas source 13 that supplies the gas. The gas supply pipe12 is provided with a mass flow controller 14, which is a flow ratecontroller for controlling a supply flow rate of the cluster generationgas.

A pressure control part 15 is provided between the mass flow controller14 and the cluster nozzle 11 to control a supply pressure of the gas tobe supplied to the cluster nozzle 11.

The pressure control part 15 includes a branch pipe 16 branched at aportion between the mass flow controller 14 and the cluster nozzle 11 inthe gas supply pipe 12, a back pressure controller 17 provided in thebranch pipe 16, and a flowmeter 18 for measuring a flow rate of the gasflowing through the branch pipe 16. The other end of the branch pipe 16is connected to the exhaust pipe 5. A pressure gauge 19 is provided atthe upstream side of the back pressure controller 17 in the branch pipe16. The back pressure controller 17 has a function of controlling apressure at the primary side, namely the upstream side of the backpressure controller 17, to a constant value. Specifically, the backpressure controller 17 includes a relief valve. When the primary-sidepressure reaches a set pressure, the relief valve is opened to exhaustexcess gas, so that the gas supply pressure is maintained at a constantpressure. The back pressure controller 17 may be any back pressurecontroller as long as it is controlled in a difference pressure mannersuch that the primary-side pressure becomes the supply pressure of thegas supplied to the cluster nozzle 11, for example, 0.9 MPa. Thepressure gauge 19 monitors a pressure at the upstream side of the backpressure controller 17. The flowmeter 18 is installed at the downstreamside of the back pressure controller 17. However, the installationposition of the flowmeter 18 is not particularly limited as long as itis capable of measuring the flow rate of the gas flowing through thebranch pipe 16.

Opening/closing valves 21 and 22 are provided at front and back sides ofthe mass flow controller 14 in the gas supply pipe 12, respectively. Anopening/closing valve 23 is provided at the downstream side of the backpressure controller 17 in the branch pipe 16.

The supply pressure of the cluster generation gas to be supplied fromthe gas source 13 to the cluster nozzle 11 is controlled by the pressurecontrol part 15 to a high pressure of, for example, 0.3 to 5.0 MPa. Whenthe cluster generation gas supplied from the gas source 13 is sprayedfrom the cluster nozzle 11 into the processing container 1 maintained ina vacuum state of, for example, 0.1 to 300 Pa, the supplied gas isadiabatically expanded so that some (several to about 10⁷) atoms ormolecules of the gas are aggregated by virtue of van der Waals force toform a gas cluster.

The cluster generation gas is not particularly limited. As an example, agas capable of generating clusters, such as a CO₂ gas, an Ar gas, an N₂gas, an SF₆ gas, a CF₄ gas or the like, may be suitably used. Aplurality of cluster generation gases may be mixed with each other andsupplied. In addition, an H₂ gas or an He gas for cluster accelerationmay be mixed with the cluster generation gas.

In order to spray the generated gas cluster onto the substrate S withoutdestroying the generated gas cluster, an internal pressure of theprocessing container 1 may be set at a low level. For example, when thesupply pressure of the gas supplied to the cluster nozzle 11 is 1 MPa orlower, the internal pressure of the processing container 1 may be 100 Paor lower, and when the supply pressure is 1 to 5 MPa, the internalpressure of the processing container 1 may be 1,000 Pa or less.

The gas cluster processing device 100 includes a control part 30. Thecontrol part 30 controls respective components (e.g., the valves, themass flow controller, the back pressure controller, and the drive part)of the gas cluster processing device 100. In particular, the controlpart 30 sends a command to set a pressure to the back pressurecontroller 17, and performs the flow control of the mass flow controller14 based on the measured flow rate of the flowmeter 18.

Next, a processing operation of the gas cluster processing device 100configured as above will be described. The gate valve 9 is opened, andthe substrate S is loaded from the vacuum transfer chamber through theloading/unloading port 8 into the processing container 1 that is beingcontinuously evacuated by the vacuum pump 6. The substrate S is placedon the substrate stage 2. Thereafter, the gate valve 9 is closed and theinternal pressure of the processing container 1 is controlled to apredetermined pressure by the pressure control valve 7.

Thereafter, the gas cluster generation gas is supplied to the clusternozzle 11 at a predetermined supply pressure. Conventionally, thecontrol of the gas supply pressure at this time has been performed bycontrolling the gas supply flow rate using a mass flow controller. Asillustrated in FIG. 2, the gas supply pressure and the gas supply flowrate is in a proportional relationship. The proportional relationshipdepends on a diameter of the orifice of the cluster nozzle. In addition,a fine adjustment of the gas supply pressure has been performed by apressure control valve (regulator) provided at the downstream side ofthe mass flow controller.

However, in the case where the gas supply pressure is controlled by thegas supply flow rate, even if the gas supply flow rate of the mass flowcontroller is set to obtain a predetermined gas supply pressure, sincethe pressure is increased in a state in which the gas flows out from theorifice of the cluster nozzle, it takes a time period until an amount ofthe gas flowing out of the orifice and an amount of the supplied gas arestabilized. Thus, as represented in FIG. 3, a time period taken to reachthe set supply pressure is prolonged. For example, when the pressure isincreased up to 0.9 MPa using a CO₂ gas as the cluster generation gas,it takes a time period of 15 minutes or more.

Meanwhile, when it is attempted to shorten the time period to reach theset supply pressure by increasing the gas supply amount to be more thanthe supply amount corresponding to the set supply pressure, the timeperiod to reach the set supply pressure is shortened compared to theprior art. However, as illustrated in FIG. 4, with respect to a desiredset pressure, the supply pressure overshoots, which may result in adegradation in pressure controllability. In addition, when such anovershoot occurs, the pressure at the downstream side of the mass flowcontroller is increased so that a difference in pressure at the frontand back sides of the mass flow controller is not obtained. This makesit difficult to control the gas supply flow rate. Even if a pressurecontrol valve (regulator) for fine adjustment of the gas supply pressureis provided at the downstream side of the mass flow controller, thepressure at the downstream side of the mass flow controller is increasedsimilarly. This makes it difficult to obtain the difference in pressureat the front and back sides of the mass flow controller, and difficultto control the gas supply flow rate.

Therefore, in the present embodiment, in order to eliminate such aproblem, the control of the gas supply pressure of the clustergeneration gas is performed using the pressure control part 15 equippedwith the back pressure controller 17.

Next, an example of a gas supply pressure controlling method will bedescribed with reference to a flowchart of FIG. 5. First, a clustergeneration gas is supplied at a first flow rate controlled by the massflow controller 14 such that the cluster generation gas is supplied at aflow rate which exceeds a flow rate required to reach a set gas supplypressure (step 1).

When the pressure reaches the set gas supply pressure, the relief valveof the back pressure controller 17 is opened to discharge excess gasthrough the branch pipe 16. The supply pressure of the clustergeneration gas supplied to the cluster nozzle 11 through the gas supplypipe 12 is maintained constant. At this time, the cleaning process ofthe substrate S begins (step 2).

After the cleaning process begins, a gas flow rate value of the branchpipe 16, which is measured by the flowmeter 18, is fed back to the massflow controller 14. The supply flow rate of the cluster generation gasis controlled to a second flow rate, which is greater than a flow rateat which the set gas supply pressure can be maintained, and which isless than the first flow rate (step 3).

As described above, the gas supply pressure itself is controlled byproviding the back pressure controller 17 in the pressure control part15 configured to control the supply pressure of the cluster generationgas. Thus, even if the cluster generation gas is supplied at a largeflow rate by the setting of the mass flow controller 14, it is possibleto discharge excess gas through the back pressure controller 17 when thesupply pressure reaches the set gas supply pressure, thereby controllingthe gas supply pressure to the set gas supply pressure. Therefore, it ispossible to supply the cluster generation gas at a large flow rate, thusallowing the gas supply pressure to reach the set gas supply pressure ina short period of time. For example, when the gas supply pressure is 0.9MPa, it taken a time period of 15 minutes or more until the set gassupply pressure is reached and stabilized from the start of the gassupply. In the present embodiment, however, it is possible to shortenthe time period to 4 minutes or less.

In addition, since the excess gas is discharged when the gas supplypressure reaches the set pressure in step 2, no overshoot occurs at thegas supply pressure. In addition, since the gas supply pressure ismaintained constant during the cleaning process by the back pressurecontroller 17, the controllability of the gas supply pressure is good.

Furthermore, after the cleaning process is started, it is possible tomeasure the flow rate of the gas flowing through the branch pipe 16 asthe excess gas using the flowmeter 18, and to control the flow rate ofthe cluster generation gas based on the measured value. Thus, it ispossible to reduce the amount of redundant gas that does not contributeto the generation of the gas cluster.

Second Embodiment

Next, a second exemplary embodiment will be described.

FIG. 6 is a cross-sectional view illustrating a gas cluster processingdevice according to the second embodiment of the present disclosure.

The basic configuration of a gas cluster processing device 101 accordingto the second embodiment is similar to that in the first embodimentshown in FIG. 1, except that the gas cluster processing device 101supplies at least two types of gases as the gas cluster generation gas.

In the present embodiment, at least two types of gases, which include atleast one type of cluster generation gas, are separately supplied asgases for generating a gas cluster. For example, two or more types ofcluster generation gases, such as the CO₂ gas, the Ar gas, the N₂ gas,the SF₆ gas, and the CF₄ gas described above, may be separatelysupplied. In some embodiments, the cluster generation gas and anacceleration gas for accelerating the cluster generation gas may besupplied individually. The acceleration gas is used when it isimpossible to obtain a required speed using the cluster generation gasalone. The acceleration gas alone is hard to generate a cluster, but hasan action of accelerating a gas cluster generated by the clustergeneration gas. As the acceleration gas, an He gas, an H₂ gas, or thelike may be used. Other gases such as a reaction gas that causes apredetermined reaction on the surface of the substrate S may be used.

In the embodiment of FIG. 6, there is shown the case in which two typesof gases are supplied using a first gas source 13 a configured to supplya first gas and a second gas source 13 b configured to supply a secondgas. Specifically, the case in which the first gas supplied from thefirst gas source 13 a is the CO₂ gas as a cluster generation gas, andthe second gas supplied from the second gas source 13 b is the H₂ gas orthe He gas as an acceleration gas, is illustrated as an example. Thefirst gas or the second gas may be a mixture of a plurality of gases.

A first pipe 12 a is connected to the first gas source 13 a, and asecond pipe 12 b is connected to the second gas source 13 b. The firstpipe 12 a and the second pipe 12 b are connected to the gas supply pipe12 extending from the cluster nozzle 11. The first gas and the secondgas, which are respectively supplied from the first gas source 13 a andthe second gas source 13 b, are joined in the gas supply pipe 12 afterpassing through the first pipe 12 a and the second pipe 12 b. The firstgas and the second gas thus joined are supplied to the cluster nozzle11. The first pipe 12 a is provided with a first mass flow controller(MFC1) 14 a, which is a flow rate controller configured to control asupply flow rate of the first gas. The second pipe 12 b is provided witha second mass flow controller (MFC2) 14 b, which is a flow ratecontroller configured to control a supply flow rate of the second gas.

In a case where three or more types of gases are supplied, gas sources,pipes, and mass flow controllers may be further provided depending onthe number of the gases.

Like the gas cluster processing device 100 of the first embodimentillustrated in FIG. 1, the gas cluster processing device 101 of thesecond embodiment also includes a pressure control part 15. The pressurecontrol part 15 is provided between the first mass flow controller 14 aand the second mass flow controller 14 b and the cluster nozzle 11, andincludes a branch pipe 16 branched from the gas supply pipe 12, a backpressure controller 17 provided in the branch pipe 16, and a flowmeter18 configured to measure a flow rate of the gas flowing through thebranch pipe 16. An opening/closing valve 23 is provided at thedownstream side of the back pressure controller 17 in the branch pipe 16as in the first embodiment.

The first pipe 12 a is provided with opening/closing valves 21 a and 22b at front and back sides of the first mass flow controller 14 a. Thesecond pipe 12 b is provided with opening/closing valves 21 b and 22 bat front and back sides of the second mass flow controller 14 b.

The gas cluster processing device 101 of the present embodiment alsoincludes a control part 30 that controls respective components (e.g.,the valves, the mass flow controllers, the back pressure controller, andthe drive part) similarly to the gas cluster processing device 100 ofthe first embodiment. In the present embodiment, the control part 30gives a command to set a pressure to the back pressure controller 17,and performs the flow rate controls of the first mass flow controller 14a and the second mass flow controller 14 b based on the flow ratesmeasured by the flowmeter 18.

Other components are the same as those of the gas cluster processingdevice 100 of the first embodiment, and thus a description thereof willbe omitted.

Next, a processing operation of the gas cluster processing device 101configured as above will be described.

Like the first embodiment, the gate valve 9 is opened and the substrateS is loaded from the vacuum transfer chamber through theloading/unloading port 8 into the processing container 1 which is beingcontinuously evacuated by the vacuum pump 6. The substrate S is placedon the substrate stage 2. Thereafter, the gate valve 9 is closed and theinternal pressure of the processing container 1 is controlled to apredetermined pressure by the pressure control valve 7.

Thereafter, at least two types of gases, which include at least one typeof cluster generation gas, are supplied to the gas cluster nozzle 11 asgases for generating a gas cluster. In the embodiment of FIG. 6, thefirst gas and the second gas are supplied from the first gas source 13 aand the second gas source 13 b, respectively.

As described above, the method of controlling the gas supply pressure bycontrolling the gas supply flow rate using the conventional mass flowcontroller when multiple types of gases are supplied has a problem inthat a gas ratio may become unstable, in addition to the problems thatthe time period taken to reach the set supply pressure is prolonged andthe controllability of the supply pressure is poor, as described above.

That is to say, as illustrated in FIG. 4 described above, when thesupply pressure overshoots, the pressure at the downstream side of themass flow controller is increased, and the difference in pressurebetween the front and back sides of the mass flow controller is notobtained. This makes it difficult to control the gas supply flow rate,and thus difficult to maintain a ratio of the multiple types of gases ata set ratio.

For example, in the case in which the CO₂ gas is used as a clustergeneration gas and the He gas or the H₂ gas is used as an accelerationgas, when the ratio of these gases deviates from the set ratio and theratio of CO₂ becomes extremely high, a partial pressure of CO₂ may beincreased in the cluster nozzle 11, which causes liquefaction in somecases. When the liquefaction of CO₂ occurs, a large cluster may begenerated, which damages a pattern on the substrate S.

In contrast, in the present embodiment, the first gas supplied from thefirst gas source 13 a is controlled by the first mass flow controller 14a, and the second gas supplied from the second gas source 13 b iscontrolled by the second mass flow controller 14 b. Thus, each of thefirst gas and the second gas is supplied at a predetermined ratio and ata flow rate exceeding an amount required to reach the set gas supplypressure. Further, the first gas and the second gas are supplied to thecluster nozzle 11 after being controlled to have the set supply pressureby the back pressure controller 17. Thus, it is possible to allow thegas supply pressure to reach the set gas supply pressure in a shortperiod of time and to control the gas supply pressure with goodcontrollability without causing the overshoot of the gas supply pressureas in the first embodiment. Furthermore, it is possible to maintain theratio of the first gas and the second gas at the set ratio withoutcausing a state in which the mass flow controller is unable to controlthe flow rate due to the overshoot of the gas supply pressure. Thisholds true in the case where three or more types of gases are used.

As in the first embodiment, after the cleaning process begins, the flowrate of the gas flowing through the branch pipe 16 as excess gas ismeasured by the flowmeter 18. The measured value is fed back to each ofthe mass flow controllers 14 a and 14 b. This makes it possible toreduce the amount of redundant gas that does not contribute to thegeneration of a gas cluster while maintaining the gas ratio.

The first flow rate, which is the set flow rate of the flow ratecontroller, may be set in a range of 1.5 times to 50 times a flow rateat which the set supply pressure can be maintained. When the first flowrate falls within the range of 50 times, it is possible to perform thecontrol in the same flow rate controller with high accuracy. When thefirst flow rate is in the range of 1.5 times to 5.0 times, it ispossible to more accurately maintain the ratio of the first gas and thesecond gas without causing an extreme change in flow speed. Thus, thefirst flow rate may fall within the range of 1.5 times to 2.0 times. Thesecond flow rate may be controlled in a range of 1.02 times to 1.5 timesa flow rate at which the predetermined gas supply pressure can bemaintained.

Third Embodiment

Next, a third embodiment will be described.

FIG. 7 is a cross-sectional view illustrating a gas cluster processingdevice according to the third embodiment of the present disclosure.

The basic configuration of a gas cluster processing device 102 of thethird embodiment is the same as that of FIG. 6 of the second embodimentexcept that the gas cluster processing device 102 includes a pressurecontrol part which is provided with two back pressure controllersarranged in series.

As illustrated in FIG. 7, in the gas cluster processing device 102 ofthe present embodiment, a pressure control part 15′ includes a branchpipe 16 branched from the gas supply pipe 12 between the mass flowcontrollers 14 a and 14 b and the cluster nozzle 11, a first backpressure controller 17 a provided in the branch pipe 16, a second backpressure controller 17 b provided at the downstream side of the firstback pressure controller 17 a in the branch pipe 16, and the flowmeter18 for measuring a flow rate of the gas flowing through the branch pipe16. The other end of the branch pipe 16 is connected to the exhaust pipe5. The position of the flowmeter 18 is not particularly limited as longas the flowmeter 18 can measure the flow rate flowing through the branchpipe 16. A first pressure gauge 19 a is provided at the upstream side ofthe first back pressure controller 17 a in the branch pipe 16, and asecond pressure gauge 19 b is provided at the upstream side of thesecond back pressure controller 17 b in the branch pipe 16. The firstpressure gauge 19 a and the second pressure gauge 19 b monitor pressuresat respective positions in the branch line 16. Opening/closing valves 23a and 23 b are provided at the downstream sides of the first backpressure controller 17 a and the second back pressure controller 17 b inthe branch pipe 16, respectively.

The first and second back pressure controllers 17 a and 17 b areserially arranged in the above manner. By setting a primary side of thesecond back pressure controller 17 b provided at the downstream side isset to be maintained at a predetermined pressure and allowing the firstback pressure controller 17 a provided at the upstream side to controlthe gas supply pressure in the gas supply pipe 12, it is possible tofurther shorten a time period until the gas supply pressure reaches theset supply pressure from the start of the gas supply and is stabilized.That is to say, by using a high-precision back pressure controllerhaving a relatively narrow difference in pressure range as the firstback pressure controller 17 a and by using a back pressure controllerhaving a relatively wide difference in pressure range as the second backpressure controller 17 b, it is possible to perform a cursory pressurecontrol using the second back pressure controller 17 b, and to performthe pressure within a narrow difference in pressure range using thefirst back pressure controller 17 a. It is therefore possible to shortenthe time until the gas supply pressure reaches the set supply pressurefrom the start of the gas supply and is stabilized, to a short period oftime of 1 minute or less.

For example, by setting a primary-side pressure (gas supply pressure) ofthe first back pressure controller 17 a to 0.9 MPa and a primary-sidepressure of the second back pressure controller 17 b to 0.75 MPa usingan electronically-controlled 40.3 MPa-pressure difference (slightpressure difference) control type of back pressure controller as thefirst back pressure controller 17 a, and a mechanically-controlled Δ1MPa-pressure difference control type of back pressure controller as thesecond back pressure controller 17 b, it is possible to reduce the timeperiod until the gas supply pressure reaches the set supply pressurefrom the start of the gas supply and is stabilized, from about 4 minutesto about 15 to 20 seconds when using a single back pressure controller.In addition, the electronically-controlled slight pressure differencetype of back pressure controller has the narrow difference in pressurerange but performs the pressure control with high accuracy at a lowerror level of ±0.01 MPa. Thus, the back pressure controller is capableof controlling the gas supply pressure with high accuracy.

Although in FIG. 7 the case of supplying multiple types of gases havebeen described as in the second embodiment, one type of gas may besupplied as in the first embodiment. In addition, three or more backpressure controllers may be provided in a serial manner.

Fourth Embodiment

Next, a fourth embodiment will be described.

FIG. 8 is a cross-sectional view illustrating a gas cluster processingdevice according to the fourth embodiment of the present disclosure.

The basic configuration of a gas cluster processing device 103 of thefourth embodiment is the same as that of FIG. 7 of the third embodiment,but differs from that of FIG. 7 in that the pressure control partfurther includes a bypass pipe for bypassing the back pressurecontrollers and an opening/closing valve that opens/closes the bypasspipe.

As illustrated in FIG. 8, in the gas cluster processing device 103 ofthe present embodiment, in addition to all the components of thepressure control part 15′ of the third embodiment illustrated in FIG. 7,a pressure control part 15″ further includes a bypass pipe 41 and anopening/closing valve 42 provided in the bypass pipe 41. One end of thebypass pipe 41 is connected to a portion of the upstream side of thefirst back pressure controller 17 a in the branch pipe 16, and the otherend thereof is connected to a portion of the downstream side of thesecond back pressure controller 17 b in the branch pipe 16, so that thebypass pipe 41 bypasses the first back pressure controller 17 a and thesecond back pressure controller 17 b.

In a case where the bypass pipe 41 and the opening/closing valve 42 arenot provided, the gas remaining in the cluster nozzle 11 and the pipe iscontinuously ejected from the cluster nozzle 11 due to the pressuredifference even if the gas supply is stopped after a substrateprocessing is completed. In general, the vacuum transfer chamberadjacent to the processing container 1 is maintained at a pressure lowerthan an internal pressure of the processing container 1. Thus, theinternal pressure of the processing container 1 needs to be furtherreduced when unloading the substrate S, which further increases thepressure difference. This prolongs a time period until the ejection ofthe gas is actually stopped from the stop of the gas supply.

The unloading of the substrate S needs to be performed after the gassupply is ceased and after the ejection of the gas from the clusternozzle 11 is stopped as described above. However, the prolonged gasejection time increases a time of replacing the substrate with a new oneafter the substrate processing is completed, which adversely affectsthroughput of the substrate processing.

In contrast, in the present embodiment, the bypass pipe 41 and theopening/closing valve 42 are provided, and the opening/closing valve 42is maintained in a closed state during the processing, and is openedafter the processing is completed. In this configuration, the gasremaining in the cluster nozzle 11 and the pipe is quickly drawn by theexhaust mechanism 10 through the bypass pipe 41. This makes it possibleto shorten a time period until the ejection of the gas from the clusternozzle 11 is stopped after the gas supply is stopped, thus shorteningthe time of replacing the substrate.

In practice, when the gas supply pressure was set to 0.9 MPa and thebypass pipe and the opening/closing valve were not used, it took 12seconds until the ejection of the gas from the cluster nozzle is stoppedafter the gas supply is stopped. In contrast, when the bypass pipe andthe opening/closing valve were used, and after stopping the gas supply,the opening/closing valve was opened to draw the gas through the bypasspipe, the time period was shortened to 2 seconds, which is ⅙ of theabove-mentioned time of 12 seconds.

Although in the gas cluster processing device 103 of FIG. 8, there isshown the case in which the bypass pipe and the opening/closing valveare added to the pressure control part of the gas cluster processingdevice 102 illustrated in FIG. 7, the bypass pipe and theopening/closing valve may be added to the gas cluster processing device100 illustrated in FIG. 1 and the gas cluster processing device 101illustrated in FIG. 6.

Fifth Embodiment

Next, a fifth embodiment will be described.

FIG. 9 is a cross-sectional view illustrating a gas cluster processingdevice according to the fifth embodiment of the present disclosure.

The basic configuration of a gas cluster processing device 104 of thefifth embodiment is the same as that of FIG. 7 of the third embodiment,but differs from that of FIG. 7 in that a booster is provided at theupstream side of a connection position at which the pressure controlpart is connected in the gas supply pipe.

As illustrated in FIG. 9, in the gas cluster processing device 104 ofthe present embodiment, a booster 45 is provided at the upstream side ofa connection portion at which the pressure control part 15′ is connectedin the gas supply pipe 12, namely a connection portion at which thebranch pipe 16 is connected to the gas supply pipe 12.

The booster 45 includes, for example, a gas booster, and is to increasea pressure of the gas supplied to the gas supply pipe 12. The booster 45is effective in increasing the supply pressure of the gas supplied tothe cluster nozzle 11.

However, in the case in which the gas supply pressure is controlled bycontrolling the gas supply flow rate using the mass flow controller asin the prior art, when the booster is used, a time period until apressure of the booster 45 is stabilized is additionally taken. Thus, inaddition to the time period taken until the amount of gas flowing outfrom the orifice of the cluster nozzle 11 and the amount of gas to besupplied are stabilized, the time period taken until the pressure of thebooster 45 is stabilized, further prolongs the time period until the gassupply pressure reaches the set supply pressure.

In contrast, in the present embodiment, it is possible to control thegas supply pressure to reach the set supply pressure in a short periodof time by controlling the gas supply pressure itself using the backpressure controller. This makes it possible to shorten the time periodrequired for stabilizing the pressure of the booster 45. Thus, byproviding the booster 45 in the present embodiment, it is possible tofurther enhance the effect of shortening the time period taken until thegas supply pressure reaches the set supply pressure from the start ofthe gas supply and is stabilized.

Although in the gas cluster processing device 104 of FIG. 9, there isshown the case in which the booster is added to the gas clusterprocessing device 102 illustrated in FIG. 7, the booster may be added tothe gas cluster processing device 100 illustrated in FIG. 1, the gascluster processing device 101 illustrated in FIG. 6, and the gas clusterprocessing device 103 illustrated in FIG. 8.

Sixth Embodiment

Next, a sixth embodiment will be described.

FIG. 10 is a cross-sectional view illustrating a gas cluster processingdevice according to the sixth embodiment of the present disclosure.

The basic configuration of a gas cluster processing device 105 of thesixth embodiment is the same as that of FIG. 7 of the third embodiment,but differs from that of FIG. 7 in that the gas cluster processingdevice 105 includes a temperature adjustment mechanism for adjusting atemperature of the cluster nozzle.

As illustrated in FIG. 10, in the gas cluster processing device 105 ofthe present embodiment, a temperature adjustment mechanism 50 isprovided in the vicinity of the cluster nozzle 11. The temperatureadjustment mechanism 50 is provided to adjust the temperature of the gassupplied to the cluster nozzle 11. It is possible to adjust the size ofthe gas cluster by heating or cooling the cluster generation gas usingthe temperature adjustment mechanism 50. Thereby, it is possible toeffectively perform the cleaning process using the gas cluster.

When the temperature of the gas is adjusted by the temperatureadjustment mechanism 50, a difference occurs between a temperature ofthe gas at the side of the gas source and a temperature of gas in thevicinity of the temperature adjustment mechanism 50 closest to thecluster nozzle 11. For example, when the temperature adjustmentmechanism 50 cools down the gas, a flow rate of the gas passing throughthe orifice of the cluster nozzle 11 is increased. Accordingly, in thiscase, there is a possibility that a desired gas supply pressure may notbe reached with a gas flow rate necessary for the cluster nozzle 11 tomaintain the gas supply pressure that is set at normal temperature (notat the time of temperature adjustment). For this reason, in the case inwhich the gas supply pressure is controlled by controlling the gassupply flow rate using the mass flow controller as in the prior art,when the temperature of the cluster nozzle 11 is changed, it isnecessary to set a gas flow rate adapted each time the temperature ofthe cluster nozzle 11 is changed. This becomes a factor to destabilizethe gas supply pressure.

In contrast, in the present embodiment, the gas supply pressure for thecluster nozzle 11 is continuously controlled to be constant by the backpressure controllers. Thus, the gas can be stably supplied even if afluctuation in temperature is caused by the temperature adjustmentmechanism 50. In addition, even if the supply gas flow rate isinsufficient or excessive, the measured value of the flowmeter 18 is fedback to the mass flow controllers 14 a and 14 b, which makes it possibleto maintain the stable gas supply.

Although in the gas cluster processing device 105 of FIG. 10, there isshown the case in which the temperature adjustment mechanism is added tothe gas cluster processing device 102 illustrated in FIG. 7, thetemperature adjustment mechanism may be applied to the gas clusterprocessing device 100 illustrated in FIG. 1, the gas cluster processingdevice 101 illustrated in FIG. 6, the gas cluster processing device 103illustrated in FIG. 8, and the gas cluster processing device 104illustrated in FIG. 9.

Experimental Example

Next, an experimental example of the present disclosure will bedescribed.

In this experimental example, the substrate processing using the gascluster was performed by the gas cluster processing device 101 of FIG.6, wherein the CO₂ gas was used as the cluster generation gas, and theH₂ gas or the He gas was used as the acceleration gas.

The substrate S was loaded into the processing container 1 in which theevacuation is being continuously performed by the vacuum pump 6. Theprimary-side pressure of the back pressure controller 17, namely the gassupply pressure, was set to 0.9 MPa. In this example, when the totalflow rate required to reach the pressure of 0.9 MPa was 1,000 sccm andthe ratio of the CO₂ gas to the H₂ gas or the He gas in flow rate wasset to 1:1, required flow rates of the CO₂ gas and the H₂ gas or the Hegas were 500 sccm in computation.

In Step 1, all the CO₂ gas and the H₂ gas or the He gas were supplied ata flow rate of 1,000 sccm, which exceeds the flow rate required to reachthe pressure that corresponds to 0.9 MPa. In Step 2, the back pressurecontroller 17 was operated to stabilize the pressure and the cleaningprocess was performed at that time. After the cleaning process wasstarted, the flow rate value measured by the flowmeter 18 was fed backto the mass flow controllers 14 a and 14 b in Step 3. The flow rate ofthe CO₂ gas and the flow rate of the H₂ gas or the He gas werecontrolled to fall within a range of more than 500 sccm to less than1,000 sccm, which is enough to maintain the gas supply pressure at 0.9MPa.

By performing the control as described above, it was possible to shortenthe time period taken until the gas supply pressure reaches the setsupply pressure from the start of the gas supply and is stabilized, inthe range of 4 minutes or below. Thus, the gas supply pressure for thecluster nozzle 11 was maintained constant. It was possible to performthe stable substrate processing.

For comparison, a substrate processing using a gas cluster was performedusing a gas cluster processing device which controls a gas supplypressure using a flow rate controlled by a mass flow controller. Asillustrated in FIG. 11, the gas cluster processing device used forcomparison includes two gas sources and two mass flow controllers, whichare the same as those in FIG. 6, and a pressure control valve 60provided in the gas supply pipe 12, instead of the pressure control part15. Reference numeral 61 denotes a pressure gauge P. In FIG. 11,components which are the same as those of FIG. 6 are denoted by the samereference numerals. The CO₂ gas was used as a cluster generation gas,and the H₂ gas or the He gas was used as an acceleration gas.

The substrate S was loaded into the processing container 1 in which theevacuation is being continuously performed by the vacuum pump 6. The gassupply pressure was set to 0.9 MPa. In this example, since the totalflow rate required to reach 0.9 MPa was 1,000 sccm in computation, theratio of the CO₂ gas and the H₂ gas or the He gas in flow rate was setto 1:1, and the flow rates of both the CO₂ gas and the H₂ gas or the Hegas were set to 500 sccm. The gases were supplied at such flow rates tocontrol the gas supply pressure. The processing was performed after thegas supply pressure was stabilized. At this time, it took 15 minutes ormore until the gas supply pressure is stabilized after the gases aresupplied.

In order to shorten the time period required to stabilize the gas supplypressure, the flow rates of the CO₂ gas and the H₂ gas or the He gaswere set to 1,000 sccm by the mass flow controllers at the start of gassupply, respectively. In this case, the time period taken to reach theset supply pressure was shortened, while the gas supply pressureovershot. In addition, the pressure at the downstream side of the massflow controller was increased at the time of occurring the overshooting.As a result, a difference in pressure at the front and back sides of themass flow controller was not obtained and a hunting phenomenon occurredin control. It was not possible to perform the flow rate control, sothat the ratio of the gases was outside of a predetermined range.

From the above results, the effects of the present disclosure wereconfirmed.

<Other Applications>

While the embodiments of the present disclosure have been describedabove, the present disclosure is not limited to the above-describedembodiments, and various modifications can be made within the scope ofthe present disclosure.

Although the case in which the substrate processing using the gascluster is applied to the cleaning process of the substrate have beendescribed in the above-mentioned embodiments, the present disclosure isnot limited thereto. As an example, the substrate processing using thegas cluster may be applied to a process such as etching. In someembodiments, various embodiments described above may be implemented inan arbitrarily combination.

EXPLANATION OF REFERENCE NUMERALS

1: processing container, 2: stage, 3: drive part, 10: exhaust mechanism,11: cluster nozzle, 12: gas supply pipe, 13, 13 a, 13 b: gas source, 14,14 a, 14 b: mass flow controller, 15, 15′, 15″: pressure controller, 16:branch pipe, 17, 17 a, 17 b: back pressure controller, 18: flowmeter,19, 19 a, 19 b: pressure gauge, 21, 22, 23, 23 a, 23 b, 42:opening/closing valve, 30: controller, 41: bypass pipe, 45: booster, 50:temperature adjustment mechanism, 100, 101, 102, 103, 104, 105: gascluster processing device, S: substrate (workpiece)

1. A gas cluster processing device for performing a predeterminedprocess on a workpiece by irradiating the workpiece with a gas cluster,comprising: a processing container in which the workpiece is disposed; agas supply part configured to supply a gas for generating the gascluster; a flow rate controller configured to control a flow rate of thegas supplied from the gas supply part; a cluster nozzle configured toreceive the gas for generating the gas cluster at a predetermined supplypressure, spray the gas into the processing container maintained in avacuum state, and convert the gas into the gas cluster through anadiabatic expansion; and a pressure control part provided in a pipebetween the flow rate controller and the cluster nozzle and including aback pressure controller configured to control a supply pressure of thegas for generating the gas cluster.
 2. The gas cluster processing deviceof claim 1, wherein the pressure control part comprises a branch pipebranched from the pipe, and further comprises as the back pressurecontroller, a first back pressure controller and a second back pressurecontroller which are provided in the branch pipe in a serial manner,wherein a high-precision back pressure controller having a relativelynarrow pressure difference range is used as the first back pressurecontroller, and a primary-side pressure of the first back pressurecontroller is set to be a set value of the gas supply pressure, andwherein a back pressure controller having a pressure difference rangewider than the pressure difference range of the first back pressurecontroller is used as the second back pressure controller, and aprimary-side pressure of the second back pressure controller is set tobe lower than the set value of the gas supply pressure.
 3. The gascluster processing device of claim 1, further comprising: a controllerconfigured to control a set flow rate of the flow rate controller,wherein the controller controls the set flow rate of the flow ratecontroller to a first flow rate exceeding a flow rate required forreaching the predetermined supply pressure until the supply pressure ofthe gas supplied from the gas supply part reaches the predeterminedsupply pressure, and wherein the pressure control part includes aflowmeter configured to measure a flow rate of a gas flowing through theback pressure controller, and wherein the controller controls, based onthe measured value obtained by the flowmeter, the set flow rate of theflow rate controller to a second flow rate which is greater than a flowrate enough to maintain the predetermined supply pressure and less thanthe first flow rate.
 4. The gas cluster processing device of claim 1,wherein the gas supply part is configured to separately supply at leasttwo types of gases as the gas for generating the gas cluster, whereinthe flow rate controller comprises at least two flow rate controllersprovided respectively to correspond to the at least two types of gases,the at least two types of gases are joined in the pipe at downstreamsides of the at least two flow rate controllers, and wherein thepressure control part is provided in a portion of the pipe in which theat least two types of gases are joined.
 5. The gas cluster processingdevice of claim 1, further comprising: a booster provided at an upstreamside of a portion of the pipe in which the pressure control part isprovided, the booster being configured to increase a pressure of the gasfor generating the gas cluster.
 6. The gas cluster processing device ofclaim 1, wherein the pressure control part further comprises: a bypassflow path provided to bypass the back pressure controller from the pipe;and an opening/closing valve configured to open/close the bypass flowpath, wherein, after the gas cluster is processed, the opening/closingvalve is opened to exhaust the gas remaining in the cluster nozzle andthe pipe through the bypass flow path.
 7. The gas cluster processingdevice of claim 3, wherein the controller is configured to control thefirst flow rate to fall within a range of 1.5 times to 50 times the flowrate enough to maintain the predetermined supply pressure, andconfigured to control the second flow rate to fall within a range of1.02 to 1.5 times the flow rate enough to maintain the predeterminedsupply pressure.
 8. A gas cluster processing method of performing apredetermined process on a workpiece by supplying a gas for generating agas cluster to a cluster nozzle through a pipe, spraying the gas fromthe cluster nozzle into a processing container maintained in a vacuumstate, converting the gas into the gas cluster by an adiabaticexpansion, and irradiating the workpiece disposed inside the processingcontainer with the gas cluster, the method comprising: controlling aflow rate of the gas to a predetermined flow rate; discharging a portionof the gas from the pipe; and controlling a supply pressure in the pipeto a predetermined supply pressure.
 9. The gas cluster processing methodof claim 8, wherein the supply pressure is controlled using a backpressure controller.
 10. The gas cluster processing method of claim 9,wherein the back pressure controller is provided in a branch pipebranched from the pipe such that the gas discharged from the pipe flowsinto the back pressure controller through the branch pipe, and wherein aprimary-side pressure of the back pressure controller is set to be thepredetermined supply pressure, and, when the primary-side pressurereaches the predetermined supply pressure, an excess gas is dischargedthrough the back pressure controller.
 11. The gas cluster processingmethod of claim 10, wherein the back pressure controller comprises afirst back pressure controller and a second back pressure controllerwhich are provided in the branch pipe in a serial manner, wherein ahigh-precision back pressure controller having a narrow pressuredifference range is used as the first back pressure controller, and theprimary-side pressure of the first back pressure controller is set to bea set value of the gas supply pressure, and wherein a back pressurecontroller having a pressure difference range wider than the pressuredifference range of the first back pressure controller is used as thesecond back pressure controller, and the primary-side pressure of thesecond back pressure controller is set to be lower than the set value ofthe gas supply pressure.
 12. The gas cluster processing method of claim8, further comprising: controlling a set flow rate of the flow ratecontroller to a first flow rate required for reaching the predeterminedsupply pressure until the supply pressure of the gas reaches thepredetermined supply pressure; measuring a flow rate of the gasdischarged from the pipe and flowing through the back pressurecontroller; and controlling, based on the measured flow rate, the flowrate of the gas to a second flow rate greater than a flow rate enough tomaintain the predetermined supply pressure and less than the first flowrate.
 13. The gas cluster processing method of claim 8, furthercomprising: separately supplying, as the gas for generating the gascluster, at least two types of gases; controlling a flow rate of each ofthe at least two types of gases; allowing the at least two types ofgases, the flow rates of which are controlled, to join with each otherin the pipe; and discharging a portion of the joined gas.
 14. The gascluster processing method of claim 8, wherein a pressure of the gas forgenerating the gas cluster is increased by a booster provided at aposition upstream of a position where the portion of the joined gas isdischarged.
 15. The gas cluster processing method of claim 12, whereinthe first flow rate is controlled to fall within a range of 1.5 times to50 times the flow rate enough to maintain the predetermined supplypressure, and the second flow rate is controlled to fall within a rangeof 1.02 to 1.5 times the flow rate enough to maintain the predeterminedsupply pressure.